1. Field of the Invention
The present invention relates to a map database apparatus employed in a navigation system that performs route guidance.
2. Description of the Related Art
Vehicular navigation systems in the known art are provided with a function for displaying a roadmap of the area where the vehicle is currently located, a function for accurately detecting the vehicle position through map matching, a function for calculating a recommended route from a point of departure to a destination, a function for performing route guidance and the like. In these vehicular navigation systems in the prior art, roadmap display data, data for map matching, data for route search and route guide data are stored in a CD ROM in order to maintain compatibility with existing software programs and also to improve the processing speed.
Route guide data stored in a map database apparatus, which include intersection names, road names and the like, are used for route guidance, and since character strings and the like are included in the route guide data, the data volume is very large, thereby necessitating efficient data processing. In addition, since an intersection is assigned a single, uniform name regardless of the direction from which the vehicle approaches the intersection, there is a problem in that accurate route guidance cannot be implemented at an intersection to which different names are assigned depending upon the direction from which it is approached.
An object of the present invention is to provide a map database apparatus that is capable of implementing accurate route guidance by causing route guide data to have directional characteristics and can be used to achieve efficient route guide data processing.
In order to attain this object, a map database apparatus according to the present invention manages roads by expressing the roads as link strings. Each of the link strings is constituted by connecting a plurality of links, each of the links has nodes at a front end and a rear end respectively, the map database apparatus has node information concerning the nodes, and the node information includes guide data to be used for route guidance. And, the guide data have directional characteristics corresponding to an order in which the links are connected.